In LTE/LTE-A system, physical cell identifiers (PCIs) are used for identifying cells, and there are a total of 504 available PCIs. Available PCIs may be allocated to cells served by all base stations in the communication system, including macro cells of macro base stations, small cells of small base stations and relaying cells of relay nodes, based on certain criteria.
Currently, according to a report on requirement vision of IMT-2020 system and related techniques from International Telecommunication Union (ITU) and Mobile and wireless communications Enablers for the Twenty-twenty Information Society (MEITS), concepts of ultra-dense network (UDN) and mobile network are introduced into the IMT-2020 system. The introduction of UDN indicates a large-scale deployment of small base stations in an IMT-2020 oriented communication system. Therefore, the number of base stations in the system will far exceed the number of available PCIs in the long term evolution/long term evolution-advanced (LTE/LTE-A) system (that is, 504). In another aspect, the deployment of small base stations is usually not planned in advance, and the number and the deployment locations of small base stations are often determined randomly, thus the network condition of the IMT-2020 communication system varies greatly depending on geographic locations. The introduction of MN indicates that mobile base station (such as a small base station which is movable) is present in the conventional communication system where base stations are stationary. When the mobile base station enters a new geographic area and one or more base stations (to which PCIs are allocated) already exist in said geographic area, there is a problem of how to allocate a PCI to the mobile base station.
Since the network condition of the IMT-2020 oriented communication system varies depending on geographic locations, and the network environment for the mobile base station constantly varies during the movement of the mobile base station, PCI conflict and confusion may occur in the geographic area in the vicinity of the mobile base station, if the PCI for the mobile base station is allocated improperly.
The conventional PCI allocation technique is directed towards stationary base stations, without considering the case where a mobile base station passes through an area with high cell density. In the area with high cell density, 504 available PCIs are often not sufficient due to the existence of a large number of base stations. Therefore, when allocating a PCI for the mobile base station entering the area, a PCI for a neighbor base station is inevitably reused, and reuse of the PCI may result in interference between two cells using the same PCI. The interference to the highly-loaded cell and the interference to the low-loaded cell have different influences to overall performance of the network. Therefore, there is a demand for a method of effectively allocating a PCI for the mobile base station, which can minimize the influence of the interference generated due to reuse of PCI.
In another aspect, since the mobile base station may experience different network environments during movement, for example, the mobile base station may move from an area with low cell density (for example, a suburban area) to an area with high cell density (for example, an urban area), the PCI for the mobile base station needs to be frequently updated to adapt to new network environment. In this case, there is a demand for a mechanism for updating the PCI for the mobile base station at a certain time interval.